Exhaust systems incorporate various components that are used to reduce pollutants in exhaust gases generated by an internal combustion engine. For example, the vehicle exhaust system is configured to remove NOx, i.e. oxides of nitrogen, from engine exhaust gases. In one known configuration, a selective catalytic reduction catalyst (SCR) is used to cause a reaction between NOx in the exhaust gas and a NOx reducing agent, such as ammonia for example. Ammonia is produced from urea by hydrolysis. To supply ammonia for this purpose, the exhaust system includes a supply of aqueous urea that is typically held within a tank.
In cold climate regions, the urea can become frozen within the tank. Certain regulations require that the urea be thawed within a predetermined amount of time. One known solution is to use an electrical heater for thawing purposes; however, this type of system has a high electrical power consumption, which is disadvantageous. Another known system uses engine coolant to heat the frozen urea; however, this does not heat the urea quickly enough.